ViewPager的TabLayout不显示标题

1) 我的tabLayout没有显示当前页面的标题。它不显示任何文本。

2) 我在viewPager中使用了相同片段的实例。每个片段从网络中获取一些数据并显示在listView中。当我在viewPager上缓慢移动页面时,所有片段都正常工作。但是,当我快速移动或使用标签到达另一个页面时,一些页面从未加载。为什么会这样?

活动:

public class WorldNews extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_world_news);

       AdView mAdView = (AdView) findViewById(R.id.adView);
       AdRequest adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest);


        // Find the view pager that will allow the user to swipe between fragments
        ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);

        // Create an adapter that knows which fragment should be shown on each page
        FragmentPageAdapter adapter = new FragmentPageAdapter(getSupportFragmentManager());

        // Set the adapter onto the view pager
        viewPager.setAdapter(adapter);

        TabLayout tabLayout = (TabLayout) findViewById(R.id.sliding_tabs);
        tabLayout.setupWithViewPager(viewPager,true);
        tabLayout.
    }
}

public class FragmentPageAdapter extends FragmentStatePagerAdapter {

    private String[] tabTitles = new String[]{"Tab1", "Tab2","Tab3" ,"Tab4" ,"Tab5","Tab6","Tab7","Tab8","Tab9","Tab10","Tab11","Tab12","Tab13","Tab14","Tab15"
            ,"Tab16","Tab17","Tab18","Tab19"};
    public FragmentPageAdapter(FragmentManager fm) {
        super(fm);
    }


    @Override
    public Fragment getItem(int position) {
        switch (position)
        {
            case 0:
                Log.d("Adapter","Case 0 called");
                return new LisViewFragment2();

            case 1:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=al-jazeera-english&sortBy=top&apiKey=6de");

            case 2:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=associated-press&sortBy=top&apiKey=6de");

            case 3:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=bbc-news&sortBy=top&apiKey=6de");

            case 4:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=cnn&sortBy=top&apiKey=6de");

            case 5:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=google-news&sortBy=top&apiKey=6de");

            case 6:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=independent&sortBy=top&apiKey=6de");

            case 7:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=metro&sortBy=top&apiKey=6de");

            case 8:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=mirror&sortBy=top&apiKey=6de");

            case 9:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=newsweek&sortBy=top&apiKey=6de");

            case 10:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=new-york-magazine&sortBy=top&apiKey=6de");

            case 11:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=reddit-r-all&sortBy=top&apiKey=6de");

            case 12:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=reuters&sortBy=top&apiKey=6de");

            case 13:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=the-guardian-uk&sortBy=top&apiKey=6de");

            case 14:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=the-hindu&sortBy=top&apiKey=6de");

            case 15:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=the-times-of-india&sortBy=top&apiKey=67de");

            case 16:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=the-new-york-times&sortBy=top&apiKey=6de");

            case 17:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=the-telegraph&sortBy=top&apiKey=6de");

            default:
                return ListViewFragment.newInstance("https://newsapi.org/v1/articles?source=usa-today&sortBy=top&apiKey=6de");


        }

    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabTitles[position];
    }

    @Override
    public int getCount() {
        return 19;
    }


}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.android.gametalks.Activity.WorldNews">


    <android.support.design.widget.TabLayout
        android:id="@+id/sliding_tabs"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
         />

<android.support.v4.view.ViewPager
    android:layout_below="@id/sliding_tabs"
    android:id="@+id/viewpager"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


</android.support.v4.view.ViewPager>



    <com.google.android.gms.ads.AdView
        xmlns:ads="http://schemas.android.com/apk/res-auto"
        android:id="@+id/adView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_alignParentBottom="true"
        ads:adSize="SMART_BANNER"
        ads:adUnitId="ca-app-pub-3940256099942544/6300978111">
    </com.google.android.gms.ads.AdView>
</RelativeLayout>

以下是片段:

public class ListViewFragment extends ListFragment implements LoaderManager.LoaderCallbacks<List<GameNews>> {

    public static ListViewFragment newInstance(String url) {
        Log.d("ListViewFragment","newInstance created");
        ListViewFragment f = new ListViewFragment();

        // Supply url input as an argument.
        Bundle args = new Bundle();
        args.putString("url", url);
        f.setArguments(args);
        return f;
    }

    List<GameNews> TotalNews;
     ListView gameListView;
     LinearLayout emptyView;
    Button retryButton;
    ListAdapter adapter ;
    private View progressBar;
    final   private int game_loader = 0;
    ArrayList<String> urls = new ArrayList<>();
    String mUrlString;
    int index;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mUrlString = getArguments().getString("url");
        urls.add(mUrlString);

        TotalNews = new ArrayList<GameNews>();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView =  inflater.inflate(R.layout.fragment_list_view, container, false);

        ArrayList<GameNews> gameList = new ArrayList<>();
        adapter = new ListAdapter(getActivity(),gameList);
        return rootView;
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        emptyView = (LinearLayout) view.findViewById(R.id.no_internet_view);
        progressBar = view.findViewById(R.id.progress_bar);
        retryButton = (Button) view.findViewById(R.id.retry_button);
        gameListView = getListView();
        emptyView.setVisibility(View.INVISIBLE);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        setListAdapter(adapter);

        //If connected to net start the loader
        if(isConnected())
        {
            getActivity().getSupportLoaderManager().restartLoader(game_loader, null, ListViewFragment.this);
            if(progressBar.getVisibility() == View.VISIBLE)
            {
                Log.d("Fragment","progress bar is still visible");
            }
        }
        //Otherwise show emptyView and hide listView
        else
        {
            emptyView.setVisibility(View.VISIBLE);
            gameListView.setVisibility(View.INVISIBLE);

        }
 }

    @Override
    public android.support.v4.content.Loader<List<GameNews>> onCreateLoader(int i, Bundle bundle) {
        AdManager manager =  new AdManager(getActivity());
        return new FragmentLoader(getActivity(),urls,1000);

    }

    @Override
    public void onLoadFinished(android.support.v4.content.Loader<List<GameNews>> loader, List<GameNews> games) {
       progressBar.setVisibility(View.INVISIBLE);
        adapter.clear();
        TotalNews.addAll(games);
        adapter.addAll(games);
       }

    @Override
    public void onLoaderReset(android.support.v4.content.Loader<List<GameNews>> loader) {
        adapter.clear();
    }

    //Method checks if there is internet
    public boolean isConnected() {
        ConnectivityManager manager = (ConnectivityManager)getActivity().getSystemService(CONNECTIVITY_SERVICE);
        NetworkInfo info = manager.getActiveNetworkInfo();
        if (info != null && info.isConnected()) {
            return true;
        }
        else {
            return false;
        }
    }
}